1. Field of the Invention
The invention involves an aircraft navigational system and a related command process.
2. Discussion of the Background
The approach phase prior to landing of an aircraft usually includes two principal stages: a descent at a considerably constant speed from a cruising altitude to an intermediate altitude (generally 3000 feet, or about 1000 m) and a deceleration while maintaining this intermediate altitude to a considerable extent. After these two principal stages, the glide slope for the airport is intercepted, and exactly to the landing strip or runway.
During deceleration, the pilot successively makes high-lift devices (=flaps and slats) evolve from a fully retracted position to a fully extended position while transitioning by intermediate positions. The progressive extension of the high-lift devices indeed permits increasing lift for the aircraft and thus permits a stable flight at lower speeds each time.
When the approach is made according to the classic arrangement mentioned above, the essence of deceleration takes place at constant altitude and the right time for extending each portion of the high-lift devices is as such relatively easy to determine for a trained pilot, by observing the sole parameter that evolves considerably, namely speed, by comparing it with the limit flight speeds (minimum and maximum) with the common configuration.
On the other hand, the classic approach process can reveal itself as annoying from the perspective of sound nuisances on the ground as a result of the progress at relatively low intermediate altitude of the aircraft over a considerable portion of its path.
As a result, it has been proposed to practice a Continuous Descent Approach (CDA), according to which the level of deceleration at constant altitude is eliminated so that the two principal stages of the classic method mentioned above are replaced by a single stage during which the aircraft descends and decelerates simultaneously; this stage is possibly broken down into several sections each having specific descent slopes.
As such, it is understood that speed and altitude vary simultaneously and can in addition, be linked one to the other in a way specific for each approach (for which the principal features are determined by the flight management system), it becomes difficult, even for an experienced pilot, to determine the right moment for extending the various configurations of the high-lift devices, by only observing the actual flight parameters.